Sleep Calculator — Best Bedtime and Wake-Up Times
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How much sleep you need by age
| Age group | Recommended sleep |
|---|---|
| Newborn (0–3 months) | 14–17 h |
| Infant (4–11 months) | 12–15 h |
| Toddler (1–2 years) | 11–14 h |
| Preschool (3–5 years) | 10–13 h |
| School age (6–13 years) | 9–11 h |
| Teen (14–17 years) | 8–10 h |
| Adult (18–64 years) | 7–9 h |
| Older adult (65+) | 7–8 h |
Ranges follow the National Sleep Foundation consensus. They describe totals, not cycle counts — a 7–9 hour target for adults works out to five or six 90-minute cycles.
Tell the calculator when your alarm goes off and it works backwards through whole 90-minute sleep cycles to suggest bedtimes that land you at the end of a cycle rather than in the middle of deep sleep. It also runs the other direction: give it a bedtime and it returns the wake-up times worth setting an alarm for. Both modes add a buffer for the time it actually takes to fall asleep, and the cycle length is adjustable because 90 minutes is an average, not a law.
How it works
- 1 Pick a direction Choose whether you know your wake-up time and need a bedtime, or know your bedtime and want the wake-up times. The 'Going to bed now' button fills in the current time and switches to wake-up mode.
- 2 Enter the time Type or pick the hour your alarm rings (or the hour you plan to be in bed). The suggestions update as you type — nothing is submitted anywhere.
- 3 Adjust the buffer if needed The default assumes 15 minutes to fall asleep and a 90-minute cycle. If you drift off in five minutes or your tracker reports shorter cycles, change both numbers and the whole list shifts.
- 4 Read the suggestions Each card shows a time, the number of complete cycles it gives you, and total sleep. The outlined cards are the 5- and 6-cycle options — 7.5 and 9 hours — which sit inside the 7–9 hour range recommended for adults.
Your data stays private
All processing happens entirely in your browser. No files, text, or data are ever sent to our servers. You can disconnect from the internet and this tool will still work.
Frequently asked questions
- How long is one sleep cycle?
- About 90 minutes on average, but real cycles run roughly 70 to 120 minutes and the first cycle of the night is usually the shortest. That's why this calculator lets you change the cycle length: if your sleep tracker consistently reports 100-minute cycles, set 100 and every suggestion moves with it.
- How does the calculator work out my bedtime?
- It subtracts whole cycles plus the fall-asleep buffer from your wake-up time. For a 7:00 alarm with 90-minute cycles and a 15-minute buffer: six cycles is 9 hours, so 7:00 − 9:00 − 0:15 gives a 21:45 bedtime. Five cycles gives 23:15, four gives 00:45, three gives 02:15.
- Why does the fall-asleep buffer matter?
- Because getting into bed is not the same as being asleep. Sleep-onset latency averages 10 to 20 minutes for healthy adults, and ignoring it shifts every cycle boundary by a quarter of an hour — enough to land your alarm in the middle of deep sleep instead of at the seam between cycles.
- Is it better to get 6 hours or 7.5 hours of sleep?
- 7.5 hours, and it isn't close. Six hours is four cycles; 7.5 is five. The extra cycle is also the one richest in REM sleep, because REM segments get longer towards morning. Cutting the night short trims REM disproportionately, which is why a short night feels worse than the missing hour suggests.
- What if I wake up between the suggested times anyway?
- That's normal — cycle length varies from night to night and from person to person, so no calculator can hit the boundary exactly. Treat the suggestions as targets rather than promises. If you routinely wake 20 minutes before your alarm, try shortening the cycle length to 85 minutes and see whether the numbers line up better.
- Should I use this for naps?
- Yes, but change the cycle length. A power nap works best at 20 to 25 minutes — short enough to stay in light sleep — while a full-cycle nap needs about 90 minutes. Anything in between tends to end during deep sleep and produces the groggy, worse-than-before feeling known as sleep inertia.
- Does anything I type get uploaded?
- No. The arithmetic runs entirely in your browser — no server call, no account, no stored history. You can load the page, go offline, and it will still work.
From the blog
Sleep Cycles, Bedtimes, and Why 7.5 Hours Beats 7 How 90-minute sleep cycles work, how to count backwards from your alarm, and the three mistakes that make sleep calculators give bad answers. Read the post →Related tools
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